This invention relates to an X-ray tube, more particularly, to a rotating anode supporting structure for an X-ray tube.
The appended FIG. 1 schematically shows a rotating anode X-ray tube 10 of a general type. It is seen that a glass envelope 12 of an X-ray tube 10 houses a cathode stem 14 and a rotating anode 16 facing the cathode stem 14. Thermoelectrons emitted from a filament 18 of the cathode stem 14 run to hit a target 20 of the rotating anode 16 resulting in heating of the target 20. For dissipation of the heat, a rotary shaft 22 having the target 20 fixed to one end thereof is rotated at such a high speed as 3000 to 12000 RPM. Accordingly, a pair of radial bearings rotatably supporting the rotary shaft 22 are heated to such a high temperature as to cause thermal deformation of the bearings. This presents a serious problem because it is very important that the axis of the rotary shaft 22 perfectly coincide with the axis of each bearing. It follows that a rotating anode supporting structure should be capable of adjusting the axes to coincide with each other even when the bearings are thermally deformed.
Known is a rotating anode supporting structure in which the tapered tip of each of three set screws engaged with the internally threaded holes of a fixed annular element of cylinder surrounding a non-rotatable outer race of a radial bearing is allowed to abut against the edge of the outer race. In the supporting structure of this type, however, each of the three set screws makes a point-contact with the edge of the outer race of the bearing. Obviously, it is imperative to arrange that each of these set screws push the edge of the outer race with equal force in order to keep the axis of the bearing perfectly coincided with the axis of the rotary shaft. Needly to say, such arrangement is extremely difficult to make. In addition, the supporting structure mentioned above is incapable of adjusting the inclination of the bearing caused by thermal deformation thereof.
Also known is a supporting structure of a rotating anode, in which a tubular nut provided with an externally threaded portion engaged with an internally threaded portion formed in the inner wall of a fixed annular element or cylinder surrounding the outer race of a bearing is allowed to push the outer race of the bearing. In this case, the flat surface at the end of the tubular nut is brought into direct contact with the outer race, rendering it very difficult for the tubular nut to push the outer race uniformly. It follows that the bearing tends to tilt and, thus, the axis of the bearing fails to coincide with the axis of the rotary shaft, rendering it very difficult to assemble satisfactorily the supporting structure. In addition, the supporting structure of this type also fails to adjust the inclination of the bearing caused by thermal deformation thereof.